1. Scope of the Invention
The present invention relates generally to films comprising silicon, oxygen and carbon formed from polyorganosilanes and methods of manufacture thereof, and more specifically to films comprising silicon, oxygen and carbon having a dielectric constant lower than 3.3 formed from polyorganosilanes films applied to substrates, and methods of manufacture thereof.
2. Related Art
As the semiconductor industry introduces new generations of integrated circuits (IC's) having higher performance and greater functionality, the density of the elements that form those IC's is increased. To bring about this density increase, the size and spacing between the individual devices or elements is reduced. While in the past such reductions were limited only by the ability to define the structures photolithographically, device geometries having dimensions as small as 0.25 micron (.mu.m) or smaller have created a new limiting factor, the dielectric constant of the insulating material(s) used between the elements. For example, for any two adjacent conductive paths, as the distance between the conductors decreases, the resulting capacitance, a function of the dielectric constant (K) of the insulating material divided by the distance between conductive paths, increases. This increased capacitance results in increased capacitive coupling between the conductors, increased power consumption and an increase in the RC time constant. Therefore, the continual improvement in semiconductor IC performance and functionality is dependent upon developing materials that form a dielectric film with a lower dielectric constant (K) than that of the most commonly used material, silicon oxide, thus resulting in reduced capacitance.
One approach for providing reduced K insulating films is doping the silicon oxide material. For example, doping silicon oxide with fluorine typically reduces K from about 3.9 to as low as 3.5. Processes for forming these doped films often advantageously use the same or similar methods that are used for forming undoped silicon oxide films. Hence the integration of fluorine doped films into the typical process flow is generally easily accomplished. However, as such fluorine doped films offer only a small decrease in K, other solutions having lower dielectric constants are needed. Also, as the doped films are formed in essentially the same manner as undoped films, planarization of films to meet photolithographic requirements is often required. Finally, the stability of such fluorine containing films with regard to moisture is problematic.
A number of families of organic polymers are another solution for providing low K dielectric films. Typically, organic polymers can form dielectric films where a K in the range of approximately 2.2-3.3 is possible. Generally, such dielectric films are formed by first applying a solution of an appropriate pre-polymer to a substrate. The substrate is then heated until the pre-polymer polymerizes to the degree desired and a solid film formed. As the organic material is applied as a liquid, some degree of surface planarization is effected and often no additional planarization is needed. However, while such organic polymer films provide both a lower dielectric constant and enhanced planarization as compared to silicon oxide films, formed for example by chemical vapor deposition, for other film properties such silicon oxide films have advantages. For example, organic materials generally have limited thermal stability above 450 degrees Centigrade (.degree. C.); they often exhibit less adhesion to common metals, such as tungsten (W) and aluminum (Al); and the mechanical strength of such organic films is much less than that of silicon oxide.
In an approach for providing a silicon oxide layer having a planar surface, spin-on glass (SOG) compositions have been prepared utilizing polyorganosilsesquioxanes; for example, see U.S. Pat. No. 4,670,299 issued to Fukuyama et al. (Fukuyama '299). The SOG compositions of Fukuyama '299 are silylated organopolysilsesquioxanes. The compositions are applied in a manner similar to that described previously for the organic polymers and then heated to form a solid polymerized film. Recently, polycarbosilanes (PCS) are used to form SOG compositions, for example, see U.S. Pat. No. 5,602,060 issued to Kobayashi et al. (Kobayashi '060). Kobayashi '060 reported that such PCS derived SOG films provide improved planarization when compared to films prepared from traditional SOG compositions, for example as per Fukuyama '299. Kobayashi '060 states that the SOG of Fukuyama '299 does not typically have a low enough viscosity to provide films with excellent planarity when applied to a substrate having topography from normal semiconductor processing. While films derived from the PCS of Kobayashi '060 might provide improved planarization when compared to those of Fukuyama '299, the final film is essentially encompasses only silicon oxide and hence cannot provide a reduced dielectric constant.
Therefore it would be advantageous to have a final dielectric film that combines the advantages of a film formed from organic materials, e.g. a low dielectric constant, with those of a film formed from inorganic materials, e.g. thermal stability. It would also be advantageous to be able to form this dielectric film from a material that is applied to a substrate in a manner essentially similar to that of an organic polymer. In addition, it would be advantageous if the final dielectric film so formed, had superior adhesion to metals such as tungsten (W) and aluminum (Al) and is thermally stable to temperatures in excess of 450 degrees Centigrade.